Diaphragm



C. MESSICK nurnnmu z n Filed Jan. 19, 19

Patented Aug. .5, 1924.

UNITED STATES 1,503,696 PATENT OFFICE.

CHARLES MESSICK, OF BBE NTWO'OD, NEW YORK.

DIAPHRAGM.

Application filed January 19, 1918, Serial No. 212,568. Renewed September 13, 1920. Serial No. 410,007.

To all whom it may concern:

Be it known that I, CHARLES MESSICK, a citizen of the United States, residing at Brentwood, in the county of Suffolk and State of New York, have invented certain new and useful Improvements in Diaphragms, of which the following is a full, clear, and exact description.

My invention relates to vibratory diaphragms of a kind suitable for general use in association with sound waves, and adapted to be operated under tension.

More particularly stated, I seek to produce a diaphragm of this type, specially adapted for recording and reproducing sounds in connection with the use of phono'graphs, the diaphragm having such form and being so built up as to present a number of advantages, both acoustical and structural.

I also seek to produce an improved stretching frame, specially constructed and adapted for producing diaphragms of the kind here contemplated.

It is a fact not generally known that if a plain flat diaphragm of large size be placed under tension by stretching it at its periphery, after the manner of tightening a drum head or a banjo head, the middle portion of the diaphragm tends to acquire a fundamental or natural tone of lower freqtlliency than other portions disposed near t e eriphery. Indeed, the middle of the diap ragm can easily have a natural tone fully an octave lower than that of other portions of the diaphragm remote from its center. As a result, the middle of the diaphragm cannot readily be forced to vibrate at a frequency high enough to record or re produce the higher notes of the musical scale. The middle portion of the dia phragm can be forced to vibrate at fre quencies suitable for the lower, notes of the scale, but this portion of the diaphragm, because of its location, is lacking in relative stifiness, and as a result the vibrations to which it may be subjected have a tendency to become localized, so that the volume of sound rendered is reduced.

I have discovered that the singular action of the diaphragm as just described is due to the fact that when the diaphragm is under tension which is apparently uniform, as for instance if the diaphragm be tightened by merely pulling its edges outwardly, the peripheral portions of the diaphragm are necessarily placed under higher tension than the middle portion. The peripheral tension is also of a character somewhat diflerent from the tension to which the middle portion is subjected. That is to say, the tensional strains to which the middle portion of the diaphragm is subjected are almost entirely radial, whereas the tensional strains affecting the peripheral portions are in great measure tangential. The net result is that the middle portion of the diaphragm is not under as high tension as portions near the periphery. This is unfortunate, especially for phonographic work, because it is customary t locate the stylus needle near the middle of the diaphragm and when so located its action is exerted most immediately upon the portion which is deficient in stiflt'ness and in self-restoring capacity.

What I seek to produce, therefore, is a diaphragm which is under tension and in which the tension strains are so distributed in direction as to extend radially outward from the center of the diaphragm, the tension strains in all other directions being eliminated as far as practicable. In other words, I endeavor to arrange the tension strains of the diaphragm in much the same manner as the tension strains of a wheel rovided with spokes under tension, and 1n. which the outer end portions of the spokes are not bound together by cross ligaments.

In a violin the strings are attached at both ends and free to vibrate between the attachments. My diaphragm is designed to vibrate like a large number of violin strings coupled together at their central portions in order that they may, vibrate synchronously; the strings collectively having sufiicient area to set into Vibration or be vibrated by the surrounding air.

Following this idea, I employ a diahragm built of thin, flat strips, each strip being subjected to tensile strain in one direction only, namely that of its len h. The strips are crossed at a central point, which thus becomes the axis or geometrical center of the diaphragm. By thus arranging the strips according to a definite system of distribution, I also give the diaphragm the proximate form of a lens, with the advantages peculiar to such form, herestretching frame, as it appears with my improved diaphragm stretched upon it.

Figure 2 is a section on the line 22 of Figure 1, looking in the direction indicated by the arrows.

Figure 3 is a section on the line 3-3 of Figure 2, and shows one of the weights used with the'stretching frame.

Figure 4 is a perspective of the finlshed diaphragm.

Extending upwardly from a pedestal 5 is a cylinder 6, carrying a spider 7 This spider is provided with a shoulder 8 of annular form.

A ring is shown at 9 and is adapted to rest upon the annular shoulder 8. This ring hecomes a part of the diaphragm, as may be understood from Figure 4.

A number of tension strips 10, 11, 12, 13, are crossed and are supported by the ring 9. Each of these tension strips is made of thin, strong, textile material, such as silk. The strips may be permeated with shellac or any suitable cementitious material, and thus caused to adhere to each other. This treatment also renders them non-porous.

By means of stitches 14 the tension strips are held together independently of any adhesive employed. The stitches 14 have another useful purpose, namely, they bind the tension strips together in such manner as to obliterate all voids and fissures that might otherwise be present. In other words, the stitches have the efiect of holding the tension strips in such form as to render the diaphragm as near solid as practicable. With this done, the tension strips are in such form that the aggregate thickness of the diaphragm at any given point is merely the added thicknesses of the several strips at such point, and the several graduations in the thickness of the diaphragm differ from each other by successive steps, each step being the thickness of a single tension strip.

I provide a number of weights 15, arranged in pairs as shown, one pair of weights being secured to the ends of each strip. Each weight carries a pair'of screw studs 16, and a clamping bar 17, as well as a pair of wing nuts 18. The wing nuts are mounted upon the screw studs, and are used to force the clamping bars against the end portions of the strips. Each clamping bar has a curved edge 19, by virtue of which the' strip is given a curved cross section where it depends from the ring 9, as may be understood from Figure 3. This arrangement insures even stretching of each strip, in the direction of the length. thereof.

A. connection 20 for a stylus mounting mayd be placed upon the diaphragm, if desire The work of construction being finished the shellac is allowed to harden so that the strips adhere to each other and to the ring 9. Then the depending end portions of the strips are cut away, so that the finished diaphragm has the appearance indicated in Figure 4. I

It will be noted that the diaphragm thus constructed has a maximum of solidity. It has no voids or interstices.

, The manner in which this result is attained may be readily understood from an inspection of Figure 1. It will be noted that according to this figure the strip 13 extends in the general direction of the length of the sheet of drawing; the strip 12 rests upon the strip 13, and extends obliquely from the upper left portion of the figure to the lower right portion thereof. The strip 11 extends from the upper right portion of the figure to the lower left portion of the same, and engages both of the strips 12 and 13. The strip 10 extends crosswise of the sheet of drawing, and engages both strips 11, 12, but not the strip 13. As may readily be noted, the middle portion of the diaphragm has a thickness equal to the aggregate thicknesses of the several strips and the diaphragm has at its outer edge a thickness which is merely the thickness of a single strip. Thus the thickness of the diaphragm is graduated, so that the diaphragm as a whole has the proximate form of a double convex lens.

The diaphragm constructed as above described overcomes the various objectionable features above pointed out. It has a comparatively high fundamental tone, and can readily respond to the soprano notes of the voice and of the musical scale. The natural or fundamental tone of any portion of the diaphragm is approximately the same as that of any other portion thereof. If the diaphragm be struck at a point adjacent its middle, the sound given off is quite'similar to that produced when the diaphragm is struck at a point comparatively near its peripheral edge.

I do not limit myself to the precise mechanism here disclosed, as variations may be made therefrom without departing from the spirit of my invention.

Where the word strip is used inthe claims, itvmeans a piece having considerably greater length than breadth.

I claim 1. A diaphragm structure including a stationary peripheral stretching frame and a vibratory portion mounted concentrically therein, said vibratory portion being tensioned at the frame along many radii and having substantially the same cross-sectional area under radial tension at all imaginary concentric sections thereof.

2. A diaphragm, including a rigid peripheral stretching frame, a vibratory portion within the frame provided with a large number of radially tensioned members of substantially the same. cross-sectional area throughout their lengths, crossing each other at the centre of the vibratory portion, and extending therefrom to the frame, like the 16 spokes of a wheel, whereby all parts of the diaphragm may be vibrated by or vibrate the centre.

3. A diaphragm provided with a peripheral stretching frame and a vibratory portion within and attached to the frame, consisting of material tensioned radially from its central portion in all directions toward the frame, substantially free from other than the radial tension and decreasing in thickness from the central portion toward the frame, whereby all parts of the vibratory portion are subjected to radial tension in proportion to thickness.

CHARLES MESSICK. 

